1. Field of the Invention
This invention relates to a novel improved optical projection viewing system. More particularly, the present invention relates to newly designed optical components which provide a wide field of view and a magnified image with a line resolution quality as good as the resolving power of the human eye.
2. Description of the Prior Art
The visual resolving power of the human eye is generally defined as being able to resolve five line pairs per millimeter at a distance of ten inches from the human eye. It is known that the resolving power of the human eye can be enhanced by interposing a magnifying optical system between the human eye and the object to be viewed.
Microscopes are employed to magnify objects at magnification powers in excess of about fifteen times to provide an enlarged image as sharp as the line resolution ability of the human eye. Modern high quality optical microscopes are capable of magnification powers of between one and two thousand times, however, at a magnification power around three hundred times the detail of the object being viewed has approached the wavelength of light. When this limit of diffraction defined by the wavelength of visibile light has been reached the additional magnification of the object being viewed is generally magnified but the detail of the object can no longer be increased due to the limit of diffraction.
Heretofore microscope optical projection viewing systems have projected a high resolution image onto a screen. My copending U.S. Pat. No. 4,449,799 filed Dec. 8, 1982 is entitled Optical Projection Viewing System and teaches the state of the art arrangement of optical components in a preferred embodiment microscope optical projection viewing system. The angle of projection of the image from the relay lens to the screen in this prior art system is achieved with the projection lenses having normal projection angles. In order to achieve high magnification of the image being projected on to the viewing screen it was necessary to project an enlarged image having a large portion projected beyond the edges of the viewing screen. If relay projection lenses of smaller projection angles had been employed to project the full image on the screen, the manification of the object being viewed would have appeared smaller. If the normal relay projection lens is retained, but the screen is brought closer to the relay projection lens, then the size of the projected image on the screen is made smaller. Even though the image is brought close to the eyes of the viewer, the overall magnification is smaller. Bringing the image closer to the eyes of the viewer decreases the field distance, which causes other problems. If the screen had been enlarged without changing the projection angle or bringing the screen closer to the relay projection lens, then the outer edges of the image would have a great amount of distortion which would be observed on the viewing screen. Enlarging the screen which is being viewed through a biocular magnifying viewing lens generates larger amounts of off-axis viewing of the field of view which also causes other problems.
If any of the aforementioned alternatives are accepted which reduce the magnification of the image on the screen, then the biocular viewing lens should be designed to make up for the lost magnification. It was found that attempts to increase the magnification of the biocular lens to increase the magnification of the image on the screen beyond a small amount created color separation and counter productive aberrations within the range of detection capability of the human eye.
When the relay lens was designed to have a smaller angle of projection to entirely project the total image onto the viewing screen, then the magnification of the object being viewed was reduced and any increase in magnification in the biocular lens to make up for this lost magnification created the same aforementioned color separation and aberrations.
It is desirable that the biocular viewing lens in a microscope optical projection viewing system have magnification, however, the eye focal distance or field distance to the object being viewed through the biocular viewing lens cannot be made so short as to induce eye strain over a period of use.
When a symmetrical biconvex biocular viewing lens was employed in an optical projection viewing system, the amount of magnification of the biocular lens could be increased by decreasing the radius of curvature of the lens surfaces, however this induced more color separation and noticeable aberrations. The color separation was the major limitation of the resolving power of such a lens. Color separation causes a black line to appear to have a blue band on one side of the line and a red band on the other side of the black line creating a fuzzy or poorly defined line.
When a symmetrical biconvex biocular viewing lens was maintained at a fixed distance from the eye of the viewer and the viewing screen is placed closer to the lens, the screen was magnified more; however, the field distance was shortened, which induced eyestrain. Moreover, the edges of the screen then appeared to be more subject to color separation and aberrations due to the increase in the off axis of field view through the viewing lens that was required to view the edges of the screen. Heretofore, ergonomic considerations in microscope optical projection viewing systems were substantially ignored in order to achieve magnification powers at the expense of field size which is not comparable with well designed high power wide field microscopes. When the magnification of the biocular viewing lens was increased, the field distance oserved by one eye was different from the field distance observed by the other eye. It has been found that both eyes attempted to shift their focus to the same field distance when viewing through a biocular viewing lens and the lenses of the eyes vacillated between the two different field distances creating a swimming sensation or vertigo. The cause of th swimming sensation or vertigo was not specifically recognized heretofore. If the eye focus shift is not severe, it only results in operator fatigue which has not been identified as being caused by eye focus shift heretofore.
If any of the optical elements of the microscope optical projection viewing system are designed for enhanced magnification and field size which induces color separation and aberrations that are observable by the operator or user of the system, then a reduction in resolution causes eyestrain, fatigue, and even vertigo.
It would be desirable to provide a microscope optical projection viewing system which has optical resolving power as good as the ability of the human eye resolving power and free from observable color separation and aberrations. It would also be desirable to provide the optical projection viewing system with a long field distance for reducing eye strain.